Antifungal Activity of Four Trichoderma Species against Phytophthora megakarya, the Causal Agent of Cocoa Pod Brown Rot in Côte d'Ivoire

Abstract

Aim. In Côte d'Ivoire, cocoa pod brown rot caused by Phytophthora megakarya represents a major constraint to sustainable cocoa production due to the severe yield losses it induces. This study aimed to evaluate the antifungal activity of four Trichoderma species (T. harzianum, T. asperellum, T. virens and T. hamatum) against P. megakarya under in vitro and in vivo conditions using detached cocoa pods. Methods. In vitro assays were conducted using a dual culture technique on PDA medium to assess the inhibition of mycelial growth of the pathogen. In vivo tests consisted of preventive treatments followed by aggressive and non-aggressive inoculations on healthy cocoa pods. Results. The in vitro results showed a significant inhibition of P. megakarya mycelial growth by all Trichoderma species, with inhibition rates ranging from 77.27% to 89.27%. Trichoderma virens exhibited the highest antagonistic activity. Under in vivo conditions, T. virens and T. harzianum significantly reduced the severity and spread of cocoa pod brown rot, with inhibition rates exceeding 80% depending on the inoculation method. Conclusions. The in vitro and in vivo assays showed that all tested species exert a significant inhibitory effect on the development of the pathogen, although the efficacy varies according to the Trichoderma species. Among the evaluated species, Trichoderma virens stood out for its strongest ability to inhibit the mycelial growth of P. megakarya and for a marked reduction in disease severity on cocoa pods under both aggressive and mild inoculation conditions. These results confirm the strong potential of Trichoderma species, particularly T. virens, as effective biocontrol agents against P. megakarya and support their integration into sustainable management strategies for cocoa pod brown rot, however, further field studies are necessary. ```